1. Field of the Invention
The invention relates to a method of producing 3-functionalized propylsilanes from hydrogen silanes and allyl compounds.
2. Background Information
Hydrogen silanes such as, for example, trichlorosilane, can be reacted in the presence of allyl compounds with the aid of platinum-containing catalysts to yield 3-chloropropylsilane. This reaction is generally designated as hydrosilylation (see, e.g., equation I). EQU Cl--CH.sub.2 --CH.dbd.CH.sub.2 +HSiCl.sub.3 .fwdarw.Cl--CH.sub.2 --CH.sub.2 --CH.sub.2 --SiCl.sub.3 (I)
The reaction can be carried out homogeneously or heterogeneously with platinum-containing catalysts. In the case of homogeneously catalyzed production, soluble platinum compounds, for example, H.sub.2 PtCl.sub.6 .times.6H.sub.2 O, are used as catalysts (DE-AS 19825793.7; DE-OS 28 51 456; CS 176 910; U.S. Pat. No. 4,292,433; U.S. Pat. No. 4,292,434; DE-AS 11 87 240; DE 11 65 028). For heterogeneous hydrosilylations, carriered platinum catalysts are used (U.S. Pat. No. 2,637,738; DE 20 12 299; DE 28 15 316).
It is known that in the reaction of, for example, allyl chloride with hydrogen silanes to 3-chloropropylsilanes, a part of the allyl chloride used reacts with the hydrogen silane in a side reaction to form propene and the particular chlorosilane (see, e.g., equation II). EQU Cl--CH.sub.2 --CH.dbd.CH.sub.2 +HSiCl.sub.3 .fwdarw.CH.sub.3 --CH.dbd.CH.sub.2 +SiCl.sub.4 (II)
During the reaction of allyl chloride with trichlorosilane, up to 25-30% of the allyl chloride used can be converted by this side reaction with trichlorosilane into propene and silicon tetrachloride. The molar ratio of chloropropylsilane to silicon tetrachloride in the raw product is a measure for the selectivity of the reaction and typically reaches values between 2.33:1 (70% yield relative to allyl chloride used) and 3:1 (75% yield).
It is furthermore known that the formation of propene can be reduced by a special reaction being carried out in pressure apparatuses; however, this method of operation has the consequence that the propene accumulating within the framework of the side reaction reacts further quantitatively with the hydrogen silane used to propylsilane. Even in the reactions carried out under normal pressure in the customary manner, the propene is converted to a considerable extent to the corresponding propylsilane (DE 34 04 703) (see, e.g., equation 3). EQU CH.sub.3 --CH.dbd.CH.sub.2 +HSiCl.sub.3 .fwdarw.CH.sub.3 --CH.sub.2 --CH.sub.2 --SiCl.sub.3 (III)
Thus, up to 230 kg propyltrichlorosilane is obtained in an industrial system in a heterogeneous, catalytic reaction of allyl chloride and trichlorosilane in a column filled with a platinum-[/]activated-carbon catalyst per 1000 kg 3-chloropropyltrichlorosilane, which results in an additional requirement of approximately 28% trichlorosilane (DE 41 19 994). In addition to the additional requirement for trichlorosilane, further problems arise because of the difficult separation and expensive removal of the undesired propylsilanes.